Imaging based calibration systems, devices, and methods

ABSTRACT

Systems, devices, and methods for imaging-based calibration of radiation treatment couch position compensations.

FIELD

The present disclosure relates generally to radiation therapy systems,devices, and methods, and more particularly to imaging-based calibrationsystems, devices, and methods for accurate target positioning andlocalization.

BACKGROUND

In radiosurgery or radiotherapy (collectively referred to as radiationtreatment) very intense and precisely collimated doses of radiation aredelivered to the target region in the body of a patient in order totreat or destroy lesions. Typically, the target region is comprised of avolume of tumorous tissue. Radiation treatment requires an accuratespatial localization of the targeted lesions. Stereotactic radiosurgery(SRS) is a specific type of image-based treatment, which delivers a highdose of radiation during a single session. Because a single radiosurgerydose is more damaging than multiple fractionated doses, the target areamust be precisely located.

In general, radiation treatments consist of several phases. First, aprecise three-dimensional (3D) map of the anatomical structures in thearea of interest (head, body, etc.) is constructed using any one of (orcombinations thereof) a computed tomography (CT), cone-beam computedtomography (CBCT), magnetic resonance imaging (MRI), positron emissiontomography (PET), 3D rotational angiography (3DRA), or ultrasoundtechniques. This determines the exact coordinates of the target withinthe anatomical structure, namely, locates the tumor or abnormalitywithin the body and defines its exact shape and size. Second, a motionpath for the radiation beam is computed to deliver a dose distributionthat the surgeon finds acceptable, taking into account a variety ofmedical constraints. During this phase, a team of specialists develop atreatment plan using special computer software to optimally irradiatethe tumor and minimize dose to the surrounding normal tissue bydesigning beams of radiation to converge on the target area fromdifferent angles and planes. Third, the radiation treatment plan isexecuted. During this phase, the radiation dose is delivered to thepatient according to the prescribed treatment plan.

The objective of radiation therapy is to accomplish tumor control whilesparing the normal tissue from radiation induced complications. This,however, requires an exact knowledge of the target position (tumorposition) not only at the planning stage but also the actual treatmenttimes. Conventionally, the tumor position is determined at one singletime during the treatment planning. This information may not, however,be accurate during treatment delivery due to patient setup errors, organmotion, and variations of the geometric parameters of the system.

The prevalence of target-conforming beams, as well as the movementtoward hypofractionation and dynamic arc IMRT, increases the need foraccurate target positioning. Image guidance provides an improvement inpositioning accuracy. Image guidance involves acquiring setup images,such as kV radiographs and/or MV portal images from multiple gantryangles, or room based X-ray systems, or MV and/or kV Cone Beam CT, aswell as in-room spiral CT's or MRI images to help target localization.If gantry and imager rotation about the isocenter would be completelyrigid and planar, the target positions determined from images frommultiple angles would be accurate. However, gantry and imager rotationabout the isocenter is not rigid and planar. Instead, a gantry head sagimposed by the weight of the gantry head, as well as similar sags in thesupports for the MV image panel, kV image panel, and kV sourcecontribute to displacements of the imaging axis and the radiation beamaxis from the isocenter. Therefore, a target position determined fromimages obtained at multiple gantry angles could be offset significantly.In order to compensate for these offsets, the deviations between thetreatment beam axis and the imaging axis need to be determined for allgantry angles and the deviations corrected.

Using a treatment couch to compensate for such deviations requires ahigh precision treatment couch, especially for high precision treatmentssuch as stereotactic radiosurgery and stereotactic body radiation.Treatment couches, however, have mechanical weaknesses which, if notcorrected, introduce errors in the accurate positioning and localizationof the target. The currently available couch compensation models thatcorrect for mechanical weaknesses, such as load dependent deflections,of the radiation treatment couches are couch dependent, and do notcorrect for installation variations or readout system productionvariations.

SUMMARY

An object of the present invention is to provide imaging-based systemsand methods for couch offset compensations which are capable of removinginstallation specific imperfections.

Another object of the present invention is to provide imaging-basedsystems and methods for positioning a treatment couch precisely to theradiation beam isocenter for all combinations of couch rotations andgantry positions.

Another object of the present invention is increasing the accuracy ofcouch compensation by taking into consideration not only the gantrydependent isocenter variations but also the effects of the treatmentcouch rotation relative to the isocenter.

Embodiments of the present disclosure provide imaging-based calibrationmethods for correcting target positions by combining gantry angledependent target position information with couch rotation angledependent couch position offset information.

Embodiments of the present disclosure further provide methods forgenerating gantry angle dependent target position information fordifferent gantry angles, and generating couch rotation angle dependentcouch position offset information for different couch rotation angles.

Embodiments of the present disclosure further provide methods forcorrecting target positions at different gantry angles and differentcouch positions by combining gantry angle dependent target positioninformation with couch rotation angle dependent couch position offsetinformation.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments will hereinafter be described with reference to theaccompanying drawings, which have not necessarily been drawn to scale.Where applicable, some features may not be illustrated to assist in theillustration and description of underlying features.

FIG. 1 illustrates a radiation treatment system according to one or moreembodiments of the disclosed subject matter.

FIG. 2 illustrates a process flow according to one or more embodimentsof the disclosed subject matter.

FIG. 3 illustrates a flow diagram of an imaging-based calibrationprocess according to one or more embodiments of the disclosed subjectmatter.

FIG. 4 illustrates an imaging-based calibration process according to oneor more embodiments of the disclosed subject matter.

FIG. 5 illustrates an imaging-based automatic target positioning methodaccording to one or more embodiments of the disclosed subject matter.

DETAILED DESCRIPTION

Patients undergoing radiation therapy are typically placed on atreatment platform of a radiation treatment gantry. The gantry has aradiation source that is used to generate a radiation beam thatirradiates a region of interest in the patient, such as a diseased issueincluding a tumor or cancerous growth site. When delivering theradiation, a plurality of radiation beams may be directed to the targetarea of interest from several positions outside the body. The gantry canbe rotated to provide the radiation beams from different positions. Thepoint at which beam trajectories converge or intersect is generallyreferred to as the isocenter. The isocenter typically receives thelargest radiation dose because of the cumulative radiation received frommultiple radiation beams. An integral part of the radiation treatmentprocess is the accurate positioning of the target volume/patient at theisocenter throughout the radiation treatment process. Setup images, suchas kV radiographs, and/or MV portal images, or room-based X-ray systemimages, or MV or kV Cone Beam CT, as well as in-room spiral CTs or MRIimages, can be acquired from multiple gantry angles to aid in theaccurate positioning of the patient. Because of the hardware flex, thehead sag imposed by the weight of the gantry head, as well as sags inthe supports for the MV image panel, kV image panel, and kV source, atarget position determined from images from multiple angles may beoffset significantly. Therefore, an integral part of the radiationtreatment process is dependent upon the calibration of the treatmentbeam axis and the imaging axis for all gantry angles. In the prior artsystems and methods, when an offset is determined between the treatmentbeam and the imaging beam, the imaging systems (on a Truebeam system,for example) or the acquired images (on Clinacs and Trilogies systems,for example) are shifted to the isocenter instead of moving thetreatment couch to correct for the offset.

In the disclosed embodiments, however, when a positioning offset isdetermined between the reference images of the target region (e.g.,volume to be treated, tumor) and the images acquired during theradiation treatment session for each gantry angle, the offset can becorrected by an operator initiated automatic couch shift from a controlroom (as shown in FIG. 2). The control room includes an imaging consoleand a LINAC console, which together constitute a treatment console.Thus, the offsets can be automatically transferred to treatment couchmotion from the treatment console.

Using a treatment couch to compensate for these offsets requires a highprecision treatment couch, especially for high precision treatments suchas stereotactic radiosurgery and stereotactic body radiation. Treatmentcouches have a high precision readout system built into them so as toallow for small couch shifts with high accuracy. The latest generationof couches (used on the Varian Truebeam Systems, for example) alsoinclude in their readout system, software to compensate for thestructural deflection of these couches caused by the elastic mechanicaldistortions of the supporting structure and internal components, whichposition deviations are not otherwise being measured by the couchreadout system. These position deviations are induced by gravity loadson the couch such as the weight of the patient and its relatedpositioning aids (breast boards, arm rests and the like). The resultingdeviations are load, as well as axis position dependent. They are alsodepending on the construction of the couch, but not on the individualcouch, or the expected manufacturing variations. These structuraldeflection compensation models are used for correcting the constructiondependent deviations of the couch, either for a typical load (forexample between 65 to 95 kg), or, for even higher accuracy, for on theactual load, which can be measured by the couch, measured externally, orinputted as a patient specific treatment parameter.

The currently available readout systems and compensation models are,however, not compensating for errors due to different installationvariations, different couch dynamics, and readout system productionvariations. Therefore, another integral part of the radiation treatmentprocess is the accurate couch positioning over large ranges, which inturn is dependent on the accurate determination of the couch offsetvalues for all couch rotation angles.

An exemplary radiation treatment system 100 that integrates radiationtreatment delivery and patient setup verification is illustrated inFIG. 1. The radiation treatment system 100 can provide radiation therapyto a patient 110 positioned on a treatment couch 102, as well asisocenter coincidence verification and couch motion offset determinationusing a calibration device, such as a phantom 110′, for example, priorto the commencement of the radiation treatment. The radiation therapytreatment can include photon-based radiation therapy, particle therapy,electron beam therapy, or any other type of treatment therapy.

In an embodiment, the radiation treatment system 100 includes aradiation treatment device 116, such as, but not limited to, aradiotherapy or radiosurgery device, which has a gantry 112 supporting aradiation module 114 with one or more radiation sources 106 and a linearaccelerator (LINAC) 104 operable to generate a beam of kilovolt (kV) ormegavolt (MV) X-ray radiation. The gantry 112 can be a ring gantry(i.e., it extends through a full 360° arc to create a complete ring orcircle), but other types of mounting arrangements may also be employed.For example, a static beam, or a C-type, partial ring gantry, or roboticarm can be used. Any other framework capable of positioning theradiation module 114 at various rotational and/or axial positionsrelative to the patient 110 may also be used.

The radiation module 114 can also include a modulation device (notshown) operable to modulate the radiation beam as well as to direct thetherapeutic radiation beam toward the patient 110 and a portion thereofthat is to be irradiated. The portion desired to be irradiated isreferred to as the target or target region or a region of interest. Thepatient 110 may have one or more regions of interest that need to beirradiated. A collimation device such as a conventional 4 jaw collimatora multileaf collimator or fixed cones or applicators (not shown) may beincluded in the modulation device to define and adjust the size of anaperture through which the radiation beam passes from radiation source106 to patient 110. The collimation device can be controlled by anactuator (not shown), which can be controlled by controller 120.

In an embodiment, the radiation therapy-treatment device 116 is a MVenergy intensity modulated radiotherapy (IMRT) device. The intensityprofiles in such a system are tailored to the treatment requirements ofthe individual patient. The IMRT fields are delivered with a multi-leafcollimator (MLC), which can be a computer-controlled mechanical beamshaping device attached to the head of the LINAC 104 and includes anassembly of metal fingers or leafs. The MLC can be made of 120 movableleafs with 0.5 cm and/or 1.0 cm leaf width, for example. For each beamdirection, the optimized intensity profile is realized by sequentialdelivery of various subfields with optimized shapes and weights. Fromone subfield to the next, the leafs may move with the radiation beam on(i.e., dynamic multi-leaf collimation (DMLC)) or with the radiation beamoff (i.e., segmented multi-leaf collimation (SMLC)). The radiationtreatment device 116 can also be a tomotherapy device where intensitymodulation is achieved with a binary collimator which opens and closesunder computer control. As the gantry 112 continuously rotates aroundthe patient 110, the exposure time of a small width of the beam can beadjusted with opening and closing of the binary collimator, allowingradiation to be delivered to the tumor through the most desirabledirections and locations of the patient.

Alternatively, the radiation treatment device 116 can be a helicaltomotherapy device, which includes a slip-ring rotating gantry or anintensity modulated arc therapy device (IMAT), which uses rotationalcone beams of varying shapes to achieve intensity modulation instead ofrotating fan beams. Indeed, any type of IMRT device can be employed asthe radiation treatment device 116. For example, embodiments of thedisclosed subject matter can be applied to image-guided radiationtherapy (IGRT) devices. Each type of radiation treatment device 116 canbe accompanied by a corresponding radiation plan and radiation deliveryprocedure.

The treatment couch 102 is positioned adjacent to the gantry 112 toplace the patient 110 and the target volume within the range ofoperation of the radiation source 106, which could be an X-ray source.The treatment couch 102 may be connected to the rotatable gantry 112 viaa communications network and is capable of translating in multipleplanes and angulations for positioning and repositioning the patient 110and the target volume. The treatment couch 102 can have three or moredegrees of freedom. The treatment couch 102 can be coupled to anautomated patient positioning system capable of manipulating the patient110 with three or more degrees of freedom (e.g., three orthogonaltranslations plus one or more rotations). In embodiments, the treatmentcouch 102 can have six (6) degrees of freedom (i.e., 6 DoF couch),namely, it can move in the vertical, lateral, longitudinal, rotation(yaw), roll, and pitch directions (x, y, z, θ₁, θ₂, θ₃). In such a case,the automated patient positioning system is capable of manipulating thepatient 110 with six degrees of freedom (e.g., three orthogonaltranslations and three rotations). In other embodiments, the treatmentcouch 102 can have four (4) degrees of freedom (i.e., 4 DoF couch),namely, it can move in the vertical, lateral, longitudinal directionsand have one rotation direction (x, y, z, θ₁). In such a case, theautomated patient positioning system is capable of manipulating thepatient 110 with four degrees of freedom (e.g., three orthogonaltranslations and one rotation).

The treatment couch 102 includes a built-in high precision readoutsystem to allow for small couch shifts with high accuracy. The readoutsystem can be a digital readout system and can include one or more couchangle encoding potentiometers, or other position and angle sensors,including, but not limited to, optical or magnetic rotary (angle) orlinear encoders. These position and angle sensors and potentiometers,supply input signals regarding the positions/movement/angle of thetreatment couch 102 to the digital readout system on the console. Theencoders include serial interface technology to provide secure datatransmission of absolute positioning values. The encoders can be fittedwith the treatment couch 102 and can be integrated with the radiationtreatment system. For example, one or more encoders can be used in themotor packages that operate in conjunction with the couch'svertical/downwards/lateral movement. Additional encoders are used forthe pitch and roll motion axis of the treatment couch 102. Each axis ofmovement can also have secondary, ‘fail-safe’ encoders, which duringsystem operation constantly check against the primary ‘master’ encodersfor successful non-stop system operation.

The readout system also includes software that integrates treatmentcouch travel and positioning with beam delivery, as well as software tocompensate for the structural deflection of the treatment couch 102caused by the elastic mechanical distortions of the supporting structureand internal components, which position deviations are not otherwisebeing measured by the readout system. These position deviations areinduced by gravity loads on the treatment couch 102 such as the weightof the patient 110 and its related positioning aids (breast boards, armrests and the like). The resulting deviations are load, as well as axisposition dependent. They are also dependent on the construction of thetreatment couch 102 and the expected couch manufacturing variations.These structural deflection compensation models are used for correctingthe construction dependent deviations of the treatment couch 102, eitherfor a typical load (for example between 65 to 95 kg), or, for evenhigher accuracy, for the actual load, which can be measured by ameasuring device integrated with the treatment couch 102, measuredexternally, or inputted as a patient specific treatment parameter. Thetreatment couch 102 can be positioned along a vertical axis at a heightwhich is at one of the height of the isocenter, above the isocenter, orbelow the isocenter.

Radiation treatment device 116 can also include a holding structure 118,which could be a robotic, servo controlled arm holding an imaging device108 for acquiring digital images. The imaging device 108 can include amegavoltage (MV) electronic portal imaging device (EPID). The imagingdevice 108 can be placed at different locations, and can generateimmediate 2-D digital information. By acquiring a plurality of MV imagesat different gantry angles, an MV-Cone beam CT image can be generatedand be used for positioning.

The radiation treatment system 100 can further include a (kV) X-rayimaging system including an X-ray source 122 and a corresponding X-raydetector/imager 124, both installed on the gantry 112 using arms 123,125 to allow for patient setup and target localization. The (kV) X-rayimaging system not only allows 2D patient setup, but it can also acquirecone beam CT (CBCT) for 3D patient setup. In general, this is done bygenerating a plurality of kV images using the (kV) X-ray imaging systemright before the start of each radiation treatment session and comparingthe generated (kV) X-ray images with corresponding patient referenceimages previously generated during the treatment planning phase. Thedetected differences between the online (kV) images (either 2D-kV imageor 3D-CBCT image) and the patient reference images (either 2D-DRR imagesor 3D-planning CT images) can be automatically transferred to treatmentcouch motion from the treatment console including controller 120, asdescribed in detail herein.

Arms 123, 125 could be electronically stabilized, robotic arms(electronic servo arms, for example) that hold the X-ray source 122 andthe X-ray detector/imager 124 in a stable configuration relative to thegantry 112. The arms 123 and 125 can have parked, partially extended,and extended positions. These positions can be programmed into thecontroller 120, and the arm positions can be extended or retractedremotely. Each of the arms 123, 125 can be controlled individually, as apair, or together with holding structure 118.

The kV X-ray imaging system can be mounted on the gantry 112 orthogonalto the imaging device 108, which could be an MV X-ray imaging device,while sharing the same isocenter of the radiation source 106. The X-raysource 122 could be an X-ray tube, and the X-ray detector/imager 124could be a high-performance flat-panel imager, for example. Both theX-ray source 122 and the X-ray detector/imager 124 could be movedlaterally and longitudinally relative to the treatment beam, and berotated through 360 degrees around the patient 110 together with theX-ray source 106 and MV X-ray imaging device 108 in both clockwise andcounterclockwise directions. The movement of the X-ray source 122 andX-ray detector/imager 124 could also be controlled by the controller120.

Controller 120 can include a computer with typical hardware such as aprocessor, and an operating system for running various software programsand/or communication applications. The computer can include softwareprograms that operate to communicate with the radiation treatment device116, which software programs are operable to receive data from externalsoftware programs and hardware. The computer can also include anysuitable input/output devices adapted to be accessed by medicalpersonnel, as well as input/output (I/O) interfaces, storage devices,memory, keyboard, mouse, monitor, printers, scanner, etc. The computercan also be networked with other computers and radiation therapysystems. Both the radiation treatment device 116 and the controller 120can communicate with a network as well as a database and servers. Thecontroller 120 can be configured to transfer medical image related databetween different pieces of medical equipment.

The radiation treatment system 100 can also include a plurality ofmodules containing programmed instructions (e.g., as part of controller120, or as separate modules within the radiation treatment system 100,or integrated into other components of the radiation treatment system100), which instructions cause the radiation treatment system 100 toperform different functions related to radiation therapy/surgery, asdiscussed herein, when executed. The radiation treatment system 100 can,for example, include a treatment delivery module operable to instructthe radiation treatment device 116 to deliver a radiation plan with orwithout the patient 110 in place; an image processing module operable toreceive images from the kV X-ray detector/imager 124 as well as the MVX-ray imaging device 108; a comparison module operable to compare theacquired kV and MV X-ray images with corresponding reference images anddetermine shifts between the kV imaging axis, the MV imaging axis, andthe radiation beam axis; an isocenter calibration module operable toalign the kV/MV imaging isocenters to the treatment isocenter based onthe comparison; a calculation module operable to determine the amount ofalignment needed (i.e., isocenter shift/offset determination); a couchoffset determination module operable to determine couch offsetinformation relative to the isocenter at each couch rotation angle; acalibration module operable to combine the gantry angle dependentisocenter offset information with the couch offset information, generategantry angle dependent couch offset information, and generate correctioninformation for all treatment couch axis based on the gantry angledependent couch offset information. The modules can be written in C orC++ programming languages, for example. Computer program code forcarrying out operations as described herein may also be written in otherprogramming languages.

The radiation treatment system 100 including the kV imaging system 122,124 and the MV X-ray imaging device 108 integrated with the radiationtreatment device 116 allows all image guidance activities, such as,image acquisition, image registration/interpretation, and patientcorrection to occur remotely. Remote couch motion allows for all axis ofthe treatment couch 102 to be adjusted remotely based on the informationgenerated by the radiation treatment system 100. Radiation treatmentsystem 100 also allows capture of all data needed for the imageacquisition (i.e., gantry angle, reference images, imager positions,type of image to be acquired (radiograph or CBCT), etc.). All data canbe transferred between different computers and radiation therapy systemsusing DICOM RT (RT Plan, RT Structure Set, RT Image Objects) as shown inFIG. 2. Although, the illustrative embodiment includes a kV imagingsystem which is integral with the gantry 112, the kV imaging system canbe a separate imaging system, such as a room based imaging system.

FIG. 2 illustrates a clinical workflow (process) using X-ray imaging forpatient/target localization. The radiation treatment includes acquiringa treatment planning scan of a patient in the treatment position in thetreatment planning room. The combination of the resulting CT images andassociated contours defines a reference CT database. The reference CTdatabase is imported to the workstation in the control room. The patientis then positioned on the treatment couch 102 in the treatment room.Localization imaging, such as, but not limited to, CBCT imaging, is thenperformed, using the X-ray imaging system. After scanning, thelocalization images are registered to the reference CT images todetermine the patient and tumor position. The alignment/fusion of thesetwo datasets may be performed using different algorithms. The result ofthe alignment is the determination of the required adjustments in thepatient/tumor positions. Once the required adjustments are determined,the necessary translations/rotations are automatically sent to thetreatment device and the treatment couch 102 is automatically moved. Theregistration information and the fusion graphic can be stored in adatabase.

Calibration Procedure

In operation, prior to radiation treatment of the patient 110, as partof an implemented quality assurance (QA) protocol, the controller 120initiates an imaging-based calibration process S100, shown in FIG. 3,that compensates for gantry angle dependent isocenter deviations as wellas couch motion offsets. The first step S101 in the imaging-basedcalibration process S100 includes a process by which the MV treatmentbeam axis, the MV imaging axis, and the kV imaging axis are calibratedto the isocenter. This process S101 can include, but is not limited to,the automated IsoCal™ calibration method (Varian Medical Systems, PaloAlto, Calif.), incorporated herein by reference in its entirety. TheIsoCal calibration method includes a combination of hardware(calibration phantom/device, collimator plate) and software toautomatically align the imaging isocenters to the treatment isocenterusing the calibration phantom and associated software.

In Step S101, a calibration device, such as a calibration phantom 110′,of known geometry, and a collimator or transmission plate with aradio-oblique pin are positioned on the treatment couch 102 in a securedknown fixed position. The calibration device (phantom) can be, but isnot limited to, an acrylic cube with engravings to indicate the centersof each surface to aid aligning the calibration cube at an isocenter.Inside the cube, at its center, a small (2 mm range) tungsten-carbide BBsphere can be positioned. One or more additional markers includingvisible and IR reflective markers can be positioned on different sidesand locations of the cube. These markers can be made of materials thatallow them to be distinguishable from the rest of the image. Any otheravailable calibration devices, such as, but not limited to, a 6D QAphantom, appropriate for kV imaging, MV imaging, and treatment andcoordinate coincidence verifications may be used. Other calibrationdevices, such as those appropriate for isocenter determination,positioning of the patient at the treatment device using various kindsof positioning and monitoring systems (kV, MV, CT, CCBCT, DTS, andoptical surface monitoring system), testing and validating themeasurement accuracy of two-dimensional (2D) and three-dimensional (3D)image measurement devices and tools installed on the radiation treatmentsystem 100, as well as verification of the measurement accuracy ofdigital image viewing stations that include diagnostic, clinical review,internet browser and teleradiology network of transferred medicaldiagnostic image systems can also be used. The calibration device(phantom) can be a three-dimensional phantom assembly that can be usedto independently verify the phantom or isocenter position by the use ofvarious positioning systems available on the treatment device, and isable to quantitatively determine the shift between the differentisocenter/imaging centers used. The calibration device is alsoconfigured to facilitate image-based positioning of the calibrationdevice using kV, MV, and optical surface monitoring.

Next, the automated isocenter calibration system and method involvesaligning the imaging isocenters (kV/MV imaging axis) to the treatmentisocenter (treatment beam axis) by imaging the calibration phantom ofknown geometry at four (4) collimator positions (the collimatorpositions can have more or less than 4 collimator positions) forexample, to find its axis, and then taking a plurality of kV X-ray andMV X-ray projection images of the calibration phantom with the kVsource/imager system 122/124, and the MV source/imager system 106/108,respectively, at a plurality of gantry angles during a 360 degreerotation of the gantry 112 around the calibration phantom 110′. In anexemplary embodiment, the gantry 112 can be rotated at an increment of 1degrees between the acquisition of each image for a complete 360 degreerotation, for example, where at zero (0) degrees, the gantry 112 ispointing to the floor, and at 180° it is pointing to the ceiling. Thegantry 112, however, can be rotated at different increments of gantryangles. The gantry 112 could also be rotated for less than 360 degrees.Alternatively, the gantry 112 can be rotated at an increment of 1degrees between the acquisition of each image for a complete 360 degreerotation, for example, where the starting position of the gantry 112 isat 180 degrees. The gantry 112, however, can be rotated at differentincrements of gantry angles. The gantry 112 could also be rotated forless than 360 degrees.

From the plurality of kV and MV projections so obtained, an algorithm,such as, but not limited to, IsoCal™ calibration algorithm can beapplied to determine the gantry 112 rotational axis and the positions ofthe three isocenters on it (kV/MV imager isocenter and MV radiationtreatment beam isocenter). The isocenters are next projected onto theimagers 108, 124 to determine correction shift vectors. The correctionshift vectors Δ_(in) (beam isocenter offsets) are 2D vectors (x, y)which indicate the lateral and longitudinal offsets, respectively,between the treatment beam isocenter and the kV/MV image centers. Thecontroller 120 can also generate a correction file including thecorrection shift vectors Δ_(in) indicating the deviations of the actualtreatment beam at each gantry angle (θ_(gn)) (i.e., gantry-angledependent deviations). These gantry-angle dependent deviations (Δ_(in))can be later applied to the MV/kV system to correct for offsets in thepositions of the imaging axis. Correcting the offsets in the positionsof the imaging axis can be done by applying the gantry-angle dependentdeviations (Δ_(in)) to the imaging system (imager arm or X-ray tube arm)or by shifting the acquired images by the amount of the gantry-angledependent deviations (Δ_(in)). Once the offsets are corrected, the exactposition of the calibration phantom in relation to the isocenter can bedetermined for each gantry angle in the range θ_(g0)-θ_(gn), where ncould be, but is not limited to, 360. By knowing the exact position ofthe calibration phantom relative to the isocenter at each gantry angle,in step S102, the position of a target relative to the isocenter can bedetermined for each gantry angle, and thus, gantry-angle dependenttarget position information (T_(n)) can be generated. The beam isocenteroffset values (Δ_(in)) together with the corresponding gantry angles(θ_(gn)) and respective gantry-angle dependent target positioninformation (T_(n)), and corresponding couch locations (C_(n)), relativeto the isocenter can be recorded in a tabular format, as a correctionfile, as shown in Table 1 below, and saved in a memory of the controller120, for example.

TABLE 1 Gantry Angle Θ_(g0) Θ_(g1) Θ_(g2) Θ_(g3) Θ_(g4) . . . . . .Θ_(gn) Θ_(gn) (degrees) Beam Isocenter Δ_(i0) Δ_(i1) Δ_(i2) Δ_(i3)Δ_(i4) . . . . . . Δ_(in) Offset Information Δ_(in) Target Position T₀T₁ T₂ T₃ T₄ . . . . . . T_(n) T_(n) relative to the isocenter CouchLocation C₀ C₁ C₂ C₃ C₄ . . . . . . C_(n) relative to isocenter C_(n)(x, y, z, θ₁, θ₂, θ₃)

Couch Rotation-Angle Dependent Couch Offset Calculation

In step S103, the couch rotation angle dependent couch position offsetinformation is generated. During this step, a plurality of megavoltageMV X-ray images of the calibration phantom are captured by the MV imager108 using MV X-rays from radiation source 106, while the treatment couch102 is rotated over its entire couch rotation range. The treatment couchrotation range includes 360 degrees, for example. However, inalternative embodiments, the treatment couch 102 rotation range caninclude less than 360 degrees. To capture the MV X-ray images, thegantry 112 is positioned at a first position, at 0 degree angle(radiation source 106 at the 12 o'clock position radiating downwards,i.e., at zero degrees the gantry 112 is pointing to the floor, and at180° it is pointing to the ceiling) for example, and the treatment couch102 is rotated in a clockwise direction from a first starting positionto its maximum rotation angle (maximum rotation angle for the treatmentcouch 102 could be, but is not limited to, 100 degrees), while imagesare acquired at 1 degree rotation angle increments. Thus, for eachdegree of treatment couch rotation, an MV X-ray image of the calibrationphantom 110′ is generated. Then, the treatment couch 102 is rotated toits maximum rotation angle in a second, counterclockwise direction,acquiring an MV X-ray image at each 1 degree rotation increment. In theexemplary embodiment, the rotation of the treatment couch 102 is in 1degree increments. However, the treatment couch 102 can be rotated atany other degree increments, such as, but not limited to, 1.5 or 2degree increments.

Next, the gantry 112 is positioned in a second position, such as between5-60 degrees or between 30 and 60 degrees, (between the 1 o'clock andthe 2 o'clock positions) for example, and the treatment couch 102 isrotated to its maximum rotation angle in the clockwise direction whileacquiring MV X-ray images of the calibration phantom 110′ at a pluralityof treatment couch rotation angles. The treatment couch 102 can berotated in 1 degree increments, and at each treatment couch rotationangle a corresponding X-ray image can be acquired. The treatment couch102 is then rotated to its maximum rotation angle in a counterclockwisedirection while acquiring MV X-ray images of the calibration phantom110′ at a plurality of treatment couch rotation angles. The treatmentcouch 102 again can be rotated 1 degrees at a time and a correspondingX-ray image generated. In the exemplary embodiment, the rotation of thetreatment couch 102 is in 1 degree increments. However, the treatmentcouch 102 can be rotated at any other degree increments, such as, butnot limited to, 1.5 or 2 degree increments.

Next, the gantry 112 is positioned in a third position, such as between300 and 355 or between 320-340 degrees (between the 10 o'clock and the11 o'clock positions), for example, and the treatment couch 102 isrotated to its maximum rotation angle in the clockwise direction whileacquiring MV X-ray images of the calibration phantom 110′ at a pluralityof treatment couch rotation angles. The treatment couch 102 can berotated in 1 degree increments, and at each treatment couch rotationangle a corresponding X-ray image can be acquired. The treatment couch102 is then rotated to its maximum rotation angle in a counterclockwisedirection while acquiring MV X-ray images of the calibration phantom110′ at a plurality of treatment couch rotation angles. The treatmentcouch 102 again can be rotated 1 degree at a time and a correspondingX-ray image generated. In the exemplary embodiment, the rotation of thetreatment couch 102 is in 1 degree increments. However, the treatmentcouch 102 can be rotated at any other degree increments, such as, butnot limited to, 1.5 or 2 degree increments.

In the illustrative embodiment, the gantry 112 is first positioned at 0degrees, then at between 30-60 degrees, then at between 300-330 degrees,respectively, prior to acquiring of the MV X-ray images. However, anyother gantry angle positions and/or combination of gantry angles arecontemplated. Therefore, the gantry 112 may start at the 0 degreeposition followed by the 300-330 degree position followed by the 30-60degree position, or any other gantry angle combination. In alternativeembodiments, the gantry 112 may be positioned only at two differentlocations. In yet other embodiments, the gantry 112 may be positioned atmore than three different locations.

In an alternative embodiment, the initial gantry position is at 180degrees (i.e., radiation is pointing to the ceiling), then the gantry112 is rotated through 360 degrees by first positioning the gantry 112at 180 degrees, then at between 210-220 degrees or between 185-240degrees, then at between 140-160 degrees or between 120-175 degrees,respectively, prior to acquiring of the MV X-ray images. However, anyother gantry angle positions and/or combination of gantry angles arecontemplated.

Each of the MV X-ray images so generated includes the markers embeddedin the calibration phantom 110′. In order to determine a position of thecalibration phantom 110′ from an X-ray image, first the positions of themarkers in the X-ray image is determined, then a one-to-onecorrespondence algorithm applied, whereby a correspondence is detectedbetween the projections of each marker in the X-ray image and themarkers themselves in the calibration phantom 110′. The positions of themarkers in an X-ray image can be determined using a conversion algorithmby which the image frame is converted to a binary image by thresholding.The binary image can then be analyzed by the controller 120 and thepositions of the markers in the generated image determined. Other knowntechniques could also be used to determine the positions of the markersin the generated X-ray image. Once the positions of the markers in theX-ray image are determined, the controller 120 can form a one-to-onecorrespondence between the projections of each marker in the X-ray imageand the markers themselves in the calibration phantom 110′. This can bedone by determining a possible orientation of the calibration phantom110′ that could produce the arrangement of the markers in the X-rayimage. The possible orientation of the calibration phantom 110′translates into possible treatment couch orientations/positions thatwould support such a calibration phantom orientation. Various otheravailable algorithms could be used for such determination. Once a matchhas been found, the estimated position of the calibration phantom 110′is determined to be the position of the calibration phantom 110′ at thecorresponding treatment couch rotation angle. By applying this imageprocessing technique for all MV X-ray images obtained, the position ofthe calibration phantom 110′ at each treatment couch rotation angle canbe determined. The MV X-ray images so generated therefore containinformation about the positions of the calibration phantom 110′ andcorresponding treatment couch positions for all treatment couch rotationangles.

The plurality of treatment couch positions for all treatment couchrotation angles obtained in step S103 are next compared to correspondingreference treatment couch positions to determine the treatment couchposition offsets for each treatment couch rotation angle. The referencetreatment couch position information can be obtained in S104 using thedigital readout system which is internal to the radiation treatmentdevice 116, or using an external readout system, which is external tothe radiation treatment device 116, but it is integrated with itsoperation.

When the internal digital readout system is used, the referencetreatment couch positions are generated during the movement of thetreatment couch 102 as described above in S103. During the movement ofthe treatment couch 102 through the treatment couch rotation angles, theposition of the treatment couch 102 for each treatment couch rotationangle is measured using the potentiometers and/or encoders integratedwith the internal digital readout system. From this, the digital readoutsystem can compute treatment couch position information for eachtreatment couch rotation angle. From this information, in S104,reference treatment couch position information (C_(m)) (x′, y′, z′, θ′₁,θ′₂, θ′₃) for all treatment couch rotation angles (θc_(n)) can begenerated.

In an alternative embodiment, an external readout system can be used togenerate the plurality of reference treatment couch locations. Such anexternal readout system could be, but is not limited to, the ExacTrac™(Brainlab Germany) or AlignRT™ (VisionRT Ltd, London UK) imaging andcontrol systems. These imaging and control systems use real-timeinfrared (IR) and X-ray (ExacTrac™), or visible light (AlignRT™) tomeasure the positions of the calibration phantom (its surface), comparethe measured positions with the detected positions, and determineposition offsets between the two.

In operation, two (Brainlab) or three (VisionRT) camera systems, mountedfrom the ceiling of the treatment room (e.g., two room based X-rayImaging Chains), record the positions of IR reflective markers on thecalibration phantom surface, or the positions of the X-ray visiblemarkers on the calibration phantom. From these images, the externalreadout system can compute 3D position information of the calibrationphantom. When the calibration phantom is moved to different locations byrotating the treatment couch 102, one degree at the time, through itsentire treatment couch rotation range (i.e., during S103), the externalreadout system can compute 3D calibration phantom position informationfor each treatment couch rotation angle. From this information, in S104,reference treatment couch position information (C_(m)) (x′, y′, z′, θ′₁,θ′₂, θ′₃) for all treatment couch rotation angles (θc_(n)) can begenerated.

The readout systems (internal and external) also include imageregistration algorithms to compare, for each treatment couch rotationangle (θc_(n)), the calibration phantom/treatment couch positioninformation obtained using the X-ray imager (S103) with a correspondingreference calibration phantom/treatment couch position informationobtained using the potentiometers and/or encoders (internal readoutsystem), or the IR or visible camera system (external readout system).The difference between the determined (i.e., measured) (C_(mn)) andreference (C_(m)) treatment couch positions for each treatment couchrotation angle (θc_(n)) can be calculated in S106. The calculatedtreatment couch position offsets (couch position offset values Δ_(cn))represent the longitudinal, lateral, vertical, and rotationaldisplacements, respectively, between the determined C_(mn) (x, y, z, θ₁,θ₂, θ₃) and the reference (C_(m)) (x′, y′, z′, θ′₁, θ′₂, θ′₃) treatmentcouch positions for every treatment couch rotation angle (θc_(n)),

where Δ_(cn)=(C_(mn))−(C_(m)); Δ_(x)=x−x′; Δy=y−y′; Δz=z−z′;Δ_(θ1)=θ₁−θ′₁; Δ_(θ2)=θ₂−θ′₂; Δ_(θ3)=θ₃−θ′₃. These offset values Δ_(cn)can be stored in a tabular format, as shown in Table 2 and saved in amemory of the controller 120, for example.

TABLE 2 Couch Rotation Θc₀ Θc₁ Θc₂ Θc₃ Θc₄ . . . . . . Θc_(n) AngleΘc_(n) (degrees) Measured C_(m0) C_(m1) C_(m2) C_(m3) C_(m4) . . . . . .C_(mn) Couch location C_(mn) (x, y, z, θ₁, θ₂, θ₃) Reference C_(r0)C_(r1) C_(r2) C_(r3) C_(r4) . . . . . . C_(rn) Couch location C_(rn)(x′, y′, z′, θ′₁, θ′₂, θ′₃) Couch location Δ_(c0) Δ_(c1) Δ_(c2) Δ_(c3)Δ_(c4) . . . . . . Δ_(cn) offset Δ_(cn) (Δ_(x), Δ_(y), Δ_(z), Δ_(θ1),Δ_(θ2), Δ_(θ3))

In step S107, the imaging-based calibration process S100 generatescorrected target position (T′_(n)) information by combining thegantry-angle dependent target position information (Table 1) with thetreatment couch rotation dependent treatment couch offset information(Table 2), as shown in Table 3. Table 3 can also be saved in a memory ofthe controller 120, for example.

By combining the information obtained from the gantry-angle dependentisocenter calibration process S101-S102 shown in Table 1, with thetreatment couch location offset information obtained from the treatmentcouch angle-dependent treatment couch position offset calculationprocess S103-S106 shown in Table 2, an accurate target positioninformation (T′_(n)) for each gantry angle/treatment couch anglecombination can be obtained, as shown in Table 3. The accurate targetposition information (T′_(n)) represents the positions of the targetafter the target has been repositioned from the original target position(T_(n)) by an amount corresponding to the treatment couch offset valuesΔ_(cn) for respective gantry angles θ_(gn) and treatment couch rotationangles Θc_(n).

TABLE 3 Gantry Angle Θ_(g0) Θ_(g1) Θ_(g2) Θ_(g3) Θ_(g4) . . . . . .Θ_(gn) Θ_(gn) (degrees) Couch Rotation Θc₀ Θc₁ Θc₂ Θc₃ Θc₄ . . . . . .Θc_(n) Angle Θc_(n) (degrees) Couch location C₀ C₁ C₂ C₃ C₄ . . . . . .C_(n) C_(n) (x, y, z, θ₁, θ₂, θ₃) Couch location Δ_(c0) Δ_(c1) Δ_(c2)Δ_(c3) Δ_(c4) . . . . . . Δ_(cn) offset Δ_(cn) (Δ_(x), Δ_(y), Δ_(z),Δ_(θ1), Δ_(θ2), Δ_(θ3)) Accurate Target T′₀ T′₁ T′₂ T′₃ T′₄ . . . . . .T′_(n) position information T′_(n) relative to the isocenter

By combining the accurate isocenter calibration of the MV treatment beam(Table 1) and the treatment couch compensation with the treatment couchoffset (Table 2), the treatment couch 102 and thus, the target, can beaccurately positioned to the beam isocenter for every combination oftreatment couch 102 rotation and gantry 112 rotation (Table 3). Variousinterpolation methods, such as, but not limited to, linearinterpolation, cubic interpolation, Hermite interpolation, trilinearinterpolation, linear regression, curve fit through arbitrary points, aswell as nearest neighbour weighted interpolation methods can be used toobtain intermediate values for these parameters, including the treatmentcouch location offset values Δ_(cn).

In alternative embodiments, the imaging-based calibration process S100can be repeated for different treatment couch loads (i.e., differentweights added to the treatment couch 102) to also calibrate for the loadoffsets. In such embodiments, for each treatment iteration, weights canbe added to the treatment couch 102 to simulate different sizedpatients, and the process steps S103-S104 repeated to generatedetermined (i.e., measured) (C_(mn)) and reference treatment couchpositions (C_(m)). The difference between the determined (i.e.,measured) (C_(mn)) and reference (C_(m)) treatment couch positions foreach treatment couch rotation angle (θc_(n)) can then be calculated inS106 by comparing the measured and reference treatment couch positionsfor each treatment couch rotation angle and for each load. Thecalculated treatment couch position offsets (treatment couch positionoffset values Δ′_(cn)) represent the longitudinal, lateral, vertical,and rotational displacements, respectively, between the determinedC_(mn) (x, y, z, θ₁, θ₂, θ₃) and the reference (C_(m)) (x′, y′, z′, θ′₁,θ′₂, θ′₃) treatment couch positions for every treatment couch rotationangle (θc_(n)) and respective treatment couch load;

where Δ′_(cn)=(C_(mn))−(C_(m)); Δ′_(x)=x−x′; Δ′y=y−y′; Δ′_(z)=z−z′;Δ′_(θ1)=θ₁−θ′₁; Δ′_(θ2)=θ₂-θ′₂; Δ′₃=θ₃−θ′₃. These offset values Δ′_(cn)can be stored in a tabular format, as shown in Table 4, and saved in amemory of the controller 120, for example.

TABLE 4 Load (lbs/kg) L₀ L₁ L₂ L₃ L₄ . . . . . . L_(n) Couch locationΔ′_(c0) Δ′_(c1) Δ′_(c2) Δ′_(c3) Δ′_(c4) . . . . . . Δ′_(cn) offsetΔ′_(cn) (Δ′_(x,) Δ′_(y), Δ′_(z), Δ′_(θ1), Δ′_(θ2), Δ′_(θ3))

In yet other embodiments, additional offsets for collimator jaw, MLC,cones as well as applicator imperfections could also be included.

FIG. 4 illustrates a process S200 by which the treatment couch 102, andthus, a target, can be accurately positioned at the isocenter for eachgantry angle, because the treatment couch imperfections introduced bythe treatment couch rotation relative to the isocenter have beencompensated for as shown herein. In step S201, the isocenter iscalibrated based on the calibration offset information stored inTable 1. Once calibrated, the positions of the target relative to theisocenter for each gantry angle can be determined in S202. Then, in stepS203, for each gantry angle, the determined target position can becorrected based on the treatment couch rotation-angle dependenttreatment couch position offset information stored in Table 3.Additionally, target position can be further corrected by applying thetreatment couch rotation-angle dependent treatment couch position offsetinformation obtained for a particular weight of the patient 110 as shownin Table 4, and thus correct for the sagging errors introduced by theweight of the patient 110.

FIG. 5 illustrates a process S300 by which, during radiation treatment,the target can be accurately and automatically positioned at theisocenter for each gantry angle based on the parameters saved in Tables1-3. As previously discussed, during treatment, a plurality of radiationbeams are directed to the target area of interest from several positionsoutside the body. The gantry 112 is rotated to provide the radiationbeams from different positions. To aid the positioning of the patient110, setup images are acquired from multiple gantry angles and thetarget position is determined from these images.

For each gantry angle, the images acquired during the radiationtreatment session (S301) are compared in S302 with previously determinedreference images of the target. When there is a difference between theacquired and reference images, it is determined that the target isoffset from the desired location. A target positioning offset is thusdetermined in S303 for each gantry angle. These offsets are corrected inS304 by an operator initiated automatic treatment couch shift from thecontrol room. In order to move the target to the correct location, foreach gantry angle θ_(gn) where a target offset is determined, the targetis first moved (S305) to a first target location T_(n), which waspreviously determined to be the isocenter for that particular gantryangle θ_(gn) (S301), as shown in Table 1. The target is moved to targetlocation T_(n) by moving the treatment couch 102 to location C_(n), asshown in Table 3. In order to compensate for errors introduced by thetreatment couch movement, the target is then automatically repositionedin S306 to location T′_(n), which represents the corrected targetlocation. The corrected target location T′_(n) represents the locationof the target after it has been moved from the initial target locationT_(n) by an amount, which equals the treatment couch rotation dependentoffset value Δ_(cn) read from Table 3 corresponding to the rotationangle θc_(n) associated with the treatment couch location C_(n). Thetarget location offsets are corrected in this way for every gantry anglewhere a target offset is detected.

Additionally, target position can be further corrected by applying thetreatment couch rotation-angle dependent treatment couch position offsetinformation obtained for a particular weight of the patient 110 as shownin Table 4, and thus correct for the treatment couch sagging errorsintroduced by the weight of the patient 110.

In yet another embodiment, the software program included in the softwaremodules of controller 120 can also include an optimization moduleoperable to optimize the treatment plan prior to and during treatmentdelivery. Optimization in real-time during treatment delivery can bettertake into account a variety of factors, such as patient anatomical andphysiological changes (e.g., respiration and other movement, etc.), andmachine configuration changes, including (e.g., beam output factors,couch error, collimator jaw and MLC imperfections and leaf errors,etc.). Real time modification of the beam intensity can account forthese changes by re-optimize beamlets in real time. The optimizationmodule can also account for cumulative errors and to adjust thetreatment plan accordingly. As such, the software can further includeoffsets for the errors introduced by collimator jaw and MLCimperfections.

It is thus apparent that an imaging-based quality assurance system andprotocol is disclosed for a radiation treatment system, comprising:performing an isocenter calibration process by using a target tocalculate deviations between a treatment beam axis and an imaging beamaxis at a plurality of gantry angles; for each gantry angle, determininga position of the target relative to the calibrated isocenter;generating treatment couch rotation angle dependent treatment couchposition offset information by: acquiring a plurality of X-ray images ofa calibration device positioned on the treatment couch at differenttreatment couch rotation angles; determining positions of the treatmentcouch at all treatment couch rotation angles based on the X-ray images;comparing each determined treatment couch position with a referencetreatment couch position for each treatment couch rotation angle;calculating treatment couch position offsets between the determined andthe reference treatment couch positions for each treatment couchrotation angle; and calibrating the position information of the targetfor each gantry angle using treatment couch rotation angle dependenttreatment couch position offset information.

It is further appreciated that the target position information can befurther calibrated using a couch compensation protocol to compensate forcouch load and position dependent mechanical deflections.

It is further to be appreciated that the system and method can furthercomprise determining offsets for collimator jaw or MLC imperfections,wherein the correcting of the target position includes correcting thetarget position by combining the gantry-angle dependent isocenter beamdeviation information with the couch rotation-angle dependent couchposition offset information, the load-dependent couch offset values, andthe offsets for collimator jaw or MLC imperfections.

It is also to be appreciated that a method for automatically positioninga target at an isocenter for each gantry angle is disclosed, comprising:generating images of the target at a plurality of gantry angles;determining a target position for each gantry angle from the acquiredimages; for each gantry angle, determining a target location offset bycomparing the acquired image for that gantry angle with a correspondingreference image; and correcting target location offset for each gantryangle by: moving the target to the isocenter; and correcting the targetlocation by moving the target by a distance which equals a previouslydetermined couch rotation dependent offset value. In embodiments, themethod can further comprise generating load-dependent couch offsetinformation by measuring errors included in the motion of the couch dueto different loads positioned thereon. The method can also furthercomprise correcting target position by combining the couchrotation-angle dependent couch position offset information with theload-dependent couch offset information.

It will be appreciated that the processes, systems, and sectionsdescribed above can be implemented in hardware, hardware programmed bysoftware, software instruction stored on a non-transitory computerreadable medium or a combination of the above. For example, a method forcan be implemented using a processor configured to execute a sequence ofprogrammed instructions stored on a non-transitory computer readablemedium. The processor can include, but not be limited to, a personalcomputer or workstation or other such computing system that includes aprocessor, microprocessor, microcontroller device, or is comprised ofcontrol logic including integrated circuits such as, for example, anApplication Specific Integrated Circuit (ASIC). The instructions can becompiled from source code instructions provided in accordance with aprogramming language such as Java, C++, C#.net or the like. Theinstructions can also comprise code and data objects provided inaccordance with, for example, the Visual Basic™ language, LabVIEW, oranother structured or object-oriented programming language. The sequenceof programmed instructions and data associated therewith can be storedin a non-transitory computer-readable medium such as a computer memoryor storage device which may be any suitable memory apparatus, such as,but not limited to read-only memory (ROM), programmable read-only memory(PROM), electrically erasable programmable read-only memory (EEPROM),random-access memory (RAM), flash memory, disk drive and the like.

Furthermore, the modules, processes, systems, and sections can beimplemented as a single processor or as a distributed processor.Further, it should be appreciated that the steps mentioned above may beperformed on a single or distributed processor (single and/ormulti-core). Also, the processes, modules, and sub-modules described inthe various figures of and for embodiments above may be distributedacross multiple computers or systems or may be co-located in a singleprocessor or system.

The modules, processors or systems described above can be implemented asa programmed general purpose computer, an electronic device programmedwith microcode, a hard-wired analog logic circuit, software stored on acomputer-readable medium or signal, an optical computing device, anetworked system of electronic and/or optical devices, a special purposecomputing device, an integrated circuit device, a semiconductor chip,and a software module or object stored on a computer-readable medium orsignal, for example.

Embodiments of the method and system (or their sub-components ormodules), may be implemented on a general-purpose computer, aspecial-purpose computer, a programmed microprocessor or microcontrollerand peripheral integrated circuit element, an ASIC or other integratedcircuit, a digital signal processor, a hardwired electronic or logiccircuit such as a discrete element circuit, a programmed logic circuitsuch as a programmable logic device (PLD), programmable logic array(PLA), field-programmable gate array (FPGA), programmable array logic(PAL) device, or the like. In general, any process capable ofimplementing the functions or steps described herein can be used toimplement embodiments of the method, system, or a computer programproduct (software program stored on a non-transitory computer readablemedium).

Furthermore, embodiments of the disclosed method, system, and computerprogram product may be readily implemented, fully or partially, insoftware using, for example, object or object-oriented softwaredevelopment environments that provide portable source code that can beused on a variety of computer platforms. Alternatively, embodiments ofthe disclosed method, system, and computer program product can beimplemented partially or fully in hardware using, for example, standardlogic circuits or a very-large-scale integration (VLSI) design. Otherhardware or software can be used to implement embodiments depending onthe speed and/or efficiency requirements of the systems, the particularfunction, and/or particular software or hardware system, microprocessor,or microcomputer being utilized.

Embodiments of the method, system, and computer program product can beimplemented in hardware and/or software using any known or laterdeveloped systems or structures, devices and/or software by those ofordinary skill in the applicable art from the function descriptionprovided herein and with a general basic knowledge of control systems,image processing and classification, and/or computer programming arts.

Moreover, embodiments of the disclosed method, system, and computerprogram product can be implemented in software executed on a programmedgeneral purpose computer, a special purpose computer, a microprocessor,or the like.

Features of the disclosed embodiments may be combined, rearranged,omitted, etc., within the scope of the invention to produce additionalembodiments. Furthermore, certain features may sometimes be used toadvantage without a corresponding use of other features.

It is thus apparent that there is provided in accordance with thepresent disclosure, an imaging-based calibration system and method forradiation treatment couch position compensations. Many alternatives,modifications, and variations are enabled by the present disclosure.While specific embodiments have been shown and described in detail toillustrate the application of the principles of the present invention,it will be understood that the invention may be embodied otherwisewithout departing from such principles. Accordingly, Applicants intendto embrace all such alternatives, modifications, equivalents, andvariations that are within the spirit and scope of the presentinvention.

The invention claimed is:
 1. A method for automatically positioning atarget at an isocenter for each gantry angle, comprising: generatingimages of the target at a plurality of gantry angles; determining atarget location for each gantry angle from the generated images; foreach gantry angle, determining a target location offset by comparing agenerated image for a gantry angle with a corresponding reference image;and correcting the target location offset for each gantry angle by:moving the target to the isocenter; and repositioning the targetlocation by moving the target by a distance which equals a previouslydetermined couch rotation dependent offset value.
 2. The method of claim1, further comprising generating load-dependent couch offset informationby measuring errors included in the motion of a couch configured to holdthe target due to different loads positioned thereon.
 3. The method ofclaim 2, further comprising correcting the target location by combiningthe previously determined couch rotation dependent offset value with theload-dependent couch offset information.
 4. The method of claim 3,further comprising determining offsets for collimator jaw or MLCimperfections, wherein the correcting of the target location includescorrecting the target location by combining the previously determinedcouch rotation dependent offset value, the load-dependent couch offsetinformation, and the offsets for collimator jaw or MLC imperfections. 5.A method for correcting a location of a target prior to irradiating thetarget with a radiation beam, comprising: positioning a target holdingdevice at a first location relative to a gantry; moving the gantry to afirst gantry angle; moving the target holding device to a secondlocation, the second location corresponding to a location corrected forisocenter movement associated with the moving of the gantry to the firstgantry angle; and correcting the second location for isocenter movementassociated with the moving of the target holding device to the secondlocation.
 6. The method of claim 5, further comprising automaticallycorrecting the location of the target.
 7. The method of claim 5, furthercomprising automatically correcting the location of the target for aplurality of gantry angles.
 8. The method of claim 7, further comprisingmoving the gantry to a plurality of gantry angles and storing isocentermovement values associated with the moving of the gantry to theplurality of gantry angles in a tabular format for later use.
 9. Themethod of claim 8, further comprising moving the target holding deviceto a plurality of locations associated with the plurality of gantryangles, and storing isocenter movement values associated with the movingof the target holding device to the plurality of locations in a tabularformat for later use.
 10. The method of claim 9, wherein theautomatically correcting the location of the target for a plurality ofgantry angles and moving of the target holding device to the pluralityof locations associated with the plurality of gantry angles comprisesautomatically correcting the location of the target for a plurality ofgantry angles and associated target holding device movements based onthe previously stored isocenter movement values.
 11. A method forirradiating a patient positioned on a treatment couch with a radiationtreatment beam from a treatment device including a gantry, comprising:positioning the treatment couch at a first location; moving the gantryto a first gantry angle; moving the treatment couch to a secondlocation, the second location corresponding to a location corrected forisocenter movement associated with the moving of the gantry to the firstgantry angle; moving the treatment couch to a third location, the thirdlocation corresponding to a location corrected for isocenter movementassociated with the moving of the treatment couch to the secondlocation; and irradiating the patient.
 12. The method of claim 11,further comprising automatically correcting patient location for aplurality of gantry angles and associated treatment couch movements. 13.The method of claim 12, further comprising moving the gantry to aplurality of gantry angles, and prerecording isocenter movement valuesassociated with the moving of the gantry to the plurality of gantryangles.
 14. The method of claim 13, further comprising moving thetreatment couch to a plurality of locations associated with theplurality of gantry angles, and prerecording isocenter movement valuesassociated with the moving of the treatment couch to the plurality oflocations.
 15. The method of claim 14, further comprising automaticallycorrecting patient location for the plurality of gantry angles based onthe prerecorded isocenter movement values.
 16. A method forautomatically positioning a target at an isocenter for a plurality ofgantry angles, comprising: generating images of the target at aplurality of gantry angles; determining target locations forcorresponding gantry angles from the generated images; for each gantryangle in the plurality of gantry angles: determining an isocenter offsetvalue by comparing a generated image for a gantry angle with acorresponding reference image; determining isocenter location based onthe determined isocenter offset value; and repositioning the target fromthe determined isocenter location by moving a couch holding the targetby a distance which equals a previously determined couch movementrelated offset value.
 17. The method of claim 16, further comprisingdetermining, for each gantry angle, a value by which the isocenterlocation shifted when the target is repositioned.
 18. The method ofclaim 17, further comprising positioning different targets on the couch,moving the couch to different locations for each target, measuringerrors introduced into movement of the couch by different weights of thedifferent targets, and generating a target-dependent offset value basedon the measured errors.
 19. The method of claim 18, further comprisingcorrecting a location of a target by combining the previously determinedcouch movement related offset value with the target-dependent offsetvalue.
 20. The method of claim 19, further comprising determining offsetvalues for collimator jaw or MLC imperfections, wherein the correctingof the location of the target includes correcting the location of thetarget by combining the previously determined couch movement relatedoffset value, the target-dependent offset value, and the offset valuesfor collimator jaw or MLC imperfections.